I have a whole series of Airinside boards. I started with buying a Formula 180 Airinside after trying windfoiling that I did not like as much as normal windsurfing on the fin. I bought the Airinside version because I wanted a board that would last longer. Before that Formula board I had a Patrik Formula V3 with full core. The difference between the full core and the Airinside was really stunning. The weight is about one kilogram lighter but the feeling is entirely different. The Airinside board is much more vivid and feels smaller than it is.
I also had a Patrik slalom 140 full core with which I was very happy in terms of performance. I used it a while and kept an eye out for the same board in Airinside version and I found it after a while. So I bought the second Airinside board, a slalom 140 Airinside V2. I bought it from a German competition windsurfer who was changing sponsors after using the board for 4 years! He told me he had a hard time letting it go because he's convinced it is the best board in its size. He changed to Duotone and after about 6 months he contacted me to ask whether he could buy the board back from me because he love it so much. I had gallon in love with it in the meantime so I kept the board and use it very often. Last Monday I was still on it for about 80 km.
After the slalom 140 I bought a slalom 115 Airinside and recently I bought a Hybrid 91 Airinside that I tested Monday and it is really nice too.
Like you say the Airinside boards feel very agile, stiff and vivid. I sometimes try a board from a friend to check whether the settings are alright and it always feels like the full core boards are heavy and sluggish but I think you get used to it very quickly if you wouldn't have an Airinside anymore.
There is certainly not a big difference in performance because otherwise we would see those boards everywhere winning races and that's not the case. But I do like the feeling of an Airinside board more than a full core board and there are others that are better surfers than me who think so too...